The present invention relates generally to an optical multiplexing/de-multiplexing system, and in particular to a micro-optic polarization beam multiplexing/de-multiplexing system which integrates polarization beam combiner/splitter (PBC) and wavelength division multiplexer/de-multiplexer (WDM) into one optical module.
Modern optical communication demands highly integrated and multi-functional optical components to achieve high performance in both long haul and metro optical networks. There is an increasing demand for an optical system with functions of both optical wavelength division multiplexing/de-multiplexing (WDM) and optical polarization division multiplexing/de-multiplexing (PDM). There are generally two approaches in the fiber optic passive component industry to meet this demand, the all fiber or fusion fiber approach and the micro-optic approach.
In all fiber or fusion fiber approach, a polarization beam combiner/splitter (PBC) can be fabricated by two polarization-maintaining (PM) fibers fused together. Thus, an all-fiber multiplexer/de-multiplexer can be fabricated as simple as a fiber coupler. U.S. Pat. No. 4,881,790 discloses an all-fiber system for coupling two pairs of polarized pumping sources with different wavelengths onto a single optical fiber for Raman pumping. In this system, two polarization selective couplers and one wavelength dependent type coupler are used to combine the two pairs of polarized pumping sources into two combined pumping sources with different wavelengths respectively and then multiplex the two combined pumping sources into one single pumping source.
In the micro-optic approach, an optical system with functions of both optical wavelength division multiplexing/de-multiplexing and optical polarization division multiplexing/de-multiplexing can be made as a combination of polarization beam combiners/splitters (PBC) and a wavelength division multiplexer/de-multiplexer (WDM). Optical polarization beam combiners/splitters (PBC) and wavelength division multiplexers/de-multiplexers (WDM) are known in the art. A micro-optic polarization beam combiner/splitter (PBC) can be as simple as a single piece of optical birefringent crystal, or thin film coating on a right angle prism (RAP), a Nicol prism, a Wollaston prism, a Rochon prism or a Sxc3xa9narmont prism. Most of these prisms are made of biregringent material wedges serving as optical polarizers. These birefringent materials comprise Calcite, YVO4, Rutile, LiNbO3 and their equivalents. A Micro-optic multiplexer/de-multiplexer is generally based on either of two mechanisms: angular dispersion or optic filtering. Two examples exhibiting angular dispersion are the prism and the blazed reflecting diffraction grating. Various wavelength-selective optical filters can also be used as an optical multiplexer/de-multiplexer.
U.S. Pat. No. 4,805,977 discloses an optical multiplexing system for combining and multiplexing two pairs of linear polarization beams into a single pumping source. In this system, a first polarization prism block combines the first pair of linear polarization beams having the same wavelength xcex1 into a first combined beam and a second polarization prism block combines the second pair of linear polarization beams having the same wavelength xcex2 into a second combined beam. An interference filter block is used to multiplex the first and second combined beams into a single pumping source. This prior art reference also discloses an optical multiplexing system for handling three pairs of linear polarization beams with different wavelengths by using three polarization prism blocks and two interference filter blocks. U.S. Pat. No. 6,052,394 discloses a high power pumping device which comprises a similar optical multiplexing system for multiplexing pumping radiations from four diodes by using two polarization beam combiners (PBC) and a wavelength division multiplexing combiner.
U.S. Pat. No. 5,740,288 discloses a variable polarization beam splitter, combiner and mixer. Each of the polarization beam combiner/splitter disclosed in this prior art reference can handle one pair of polarized beams. If two or more pairs of polarized beams with different wavelengths need to be combined, two or more polarization beam combiners are still needed.
In both existing approaches, it is a common drawback that an optical system with functions of both optical wavelength division multiplexing/de-multiplexing (WDM) and optical polarization division multiplexing/de-multiplexing (PDM) is made by simply cascading the function blocks of polarization beam combiner/splitter (PBC) and wavelength division multiplexer/de-multiplexer (WDM) in series. When the number of beams or the complexity of the optical system increases, the number of optical components and the size of the optical system increase accordingly while the total performance decreases.
In view of the above, it would be an advance in the art to provide a micro-optic multiplexing/de-multiplexing which is more compact, less components, high performance and cost-effective. It would be an especially welcome advance to provide a micro-optic multiplexing/de-multiplexing system that integrates one polarization beam combiner/splitter (PBC) and one wavelength division multiplexer/de-multiplexer (WDM), e.g. an optical filter, into one optical module that can handle two or more pairs of polarization-perpendicular beams of different wavelengths.
It is a primary object of the present invention to provide a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using only one polarization beam combiner and a filter.
It is a further primary object of the present invention to provide a micro-optic polarization beam de-multiplexing system for de-multiplexing an input beam with two different wavelengths into two polarization-perpendicular pairs of beams of different wavelengths by using only one filter and one polarization beam splitter.
It is another object of the present invention to provide a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using one polarizing prism as the polarization beam combiner and a filter. The polarizing prism can be selected from a group consisting of Wollaston prism, Rochon prism, Sxc3xa9narmont prism and their equivalents.
It is another object of the present invention to provide a micro-optic polarization beam de-multiplexing system for de-multiplexing an input beam with two different wavelengths into two polarization-perpendicular pairs of beams of different wavelengths by using only one filter and one polarizing prism as the polarization beam splitter. The polarizing prism can be selected from a group consisting of Wollaston prism, Rochon prism, Sxc3xa9narmont prism and their equivalents.
It is a further object of the present invention to provide a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using one polarization beam combiner and a filter. The polarization beam combiner has two optical wedges and a Faraday rotator disposed between the two wedges.
It is another object of the present invention to provide a micro-optic polarization beam de-multiplexing system for de-multiplexing an input beam with two different wavelengths into two polarization-perpendicular pairs of beams of different wavelengths by using one filter and one polarization beam splitter. The polarization beam splitter has two optical wedges and a Faraday rotator disposed between the two wedges.
It is yet another object of the present invention to provide a micro-optic multiplexing system for pumping high gain Raman amplifiers and Erbium-doped fiber amplifiers (EDFA).
The micro-optic polarization beam multiplexing/de-multiplexing system of the present invention is not limited to handle two polarization-perpendicular pairs of beams of different wavelengths. By any cascading or combining techniques familiar to those skilled in the art, the micro-optic system of the present invention can be easily extended to handle three or more pairs of beams with different wavelengths.
As the micro-optic polarization beam multiplexing/de-multiplexing system of the present invention integrates the polarization beam combiner/splitter, wavelength division multiplexer/de-multiplexer (WDM), and even isolator into one optical module, it is of higher performance, less components, lower loss, lower cost and smaller footprint.
These and numerous other objects and advantages of the present invention will become apparent upon reading the detailed description.
In accordance with the present invention, a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam is provided. The micro-optic system has a first collimating means for introducing a first input ordinary beam with wavelength xcex1o of a first pair of input beams, a second collimating means for introducing a first input extraordinary beam with wavelength xcex1e of the first pair of input beams, a third collimating means for introducing a second input ordinary beam with wavelength xcex2o of a second pair of input beams, a fourth collimating means for introducing a second input extraordinary beam with wavelength xcex2e of the second pair of input beams, a polarization beam combiner for combining the first pair of input beams and the second pair of input beams into a first combined light beam with wavelength xcex1 and a second combined light beam with wavelength xcex2, and a filter for multiplexing the first combined light beam and the second combined light beam into an output beam with wavelength xcex1 and wavelength xcex2. The wavelength xcex1 equals to the wavelength xcex1o and the wavelength xcex1e, and the wavelength xcex2 equals to the wavelength xcex2o and the wavelength xcex2e. The micro-optic system also has a fifth collimating means for receiving the output beam.
The micro-optic system of the present invention further has a first subassembly holding an end of a first fiber, a second subassembly holding an end of a second fiber, a third subassembly holding an end of a third fiber, a fourth subassembly holding an end of a fourth fiber, and a fifth subassembly holding an end of a fifth fiber. Each subassembly is in paraxial relationship with the corresponding collimating means. The first fiber, the second fiber, the third fiber and the fourth fiber are polarization-maintaining optical fibers, and the fifth fiber is a single mode optical fiber. The filter can be disposed before, after or inside the polarization beam combiner.
It is apparent to those skilled in the art that this micro-optic system can be used inversely as a micro-optic de-multiplexing system for de-multiplexing an input beam with wavelength xcex1 and wavelength xcex2 into a first pair of output beams comprising a first output ordinary beam with wavelength xcex1o and a first output extraordinary beam with wavelength xcex1e and a second pair of output beams comprising a second output ordinary beam with wavelength xcex2o and a second output extraordinary beams with wavelength xcex2e.
In accordance with the present invention, there is further provided a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using a polarizing prism as the polarization beam combiner. The micro-optic system has a first collimating means for introducing a first input ordinary beam with wavelength xcex1o of a first pair of input beams, a second collimating means for introducing a first input extraordinary beam with wavelength xcex1e of the first pair of input beams, a third collimating means for introducing a input second ordinary beam with wavelength xcex2o of a second pair of input beams, and a fourth collimating means for introducing a second input extraordinary beam with wavelength xcex2e of the second pair of input beams.
The polarizing prism of the micro-optic polarization beam multiplexing system has a first half and a second half. The first half has a first external surface and a second external surface and the second half has a third external surface opposing to the second external surface and a fourth external surface opposing to the first external surface. The centers of the second external surface and the third external surface define an optical axis. The first half combines the first pair of input beams that are incident on the first external surface into a first combined light beam with wavelength xcex1. The second half and the first half combining the first pair of input beams that are incident on the third external surface into a second combined light beam with wavelength xcex2. A filter is disposed between the first half and the second half to reflect light beam with wavelength xcex1 and be transparent to light beam with wavelength xcex2, thereby the filter multiplexing the first combined light beam and the second combined light beam into an output beam along the optical axis. The wavelength xcex1 equals to the wavelength xcex1o and the wavelength xcex1e, and the wavelength xcex2 equals to the wavelength xcex2o and the wavelength xcex2e. The micro-optic system also has a fifth collimating means for receiving the output beam.
The micro-optic system further has a first subassembly holding an end of a first fiber, a second subassembly holding an end of a second fiber, a third subassembly holding an end of a third fiber, a fourth subassembly holding an end of a fourth fiber, and a fifth subassembly holding an end of a fifth fiber. Each subassembly is in paraxial relationship with the corresponding collimating means. The first fiber, the second fiber, the third fiber and the fourth fiber are polarization-maintaining optical fibers, and the fifth fiber is a single mode optical fiber. The polarizing prism can be selected from a group consisting of Wollaston prism, Rochon prism, Sxc3xa9narmont prism and their equivalents. A rotator can also be disposed between the two halves of the polarizing prism before or after the filter.
It is also apparent to those skilled in the art that this micro-optic system with a polarizing prism and a filter can be used inversely as a micro-optic de-multiplexing system for de-multiplexing an input beam with wavelength xcex1 and wavelength xcex2 into a first pair of output beams comprising a first output ordinary beam with wavelength xcex1o and a first output extraordinary beam with wavelength xcex1e and a second pair of output beams comprising a second output ordinary beam with wavelength xcex2o and a second output extraordinary beams with wavelength xcex2e.
In accordance with the present invention, there is also provided a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using two optical wedges and a Faraday rotator as the polarization beam combiner.
The micro-optic polarization beam multiplexing system has a first collimating means for introducing a first input ordinary beam with wavelength xcex1o of a first pair of input beams, a second collimating means for introducing a first input extraordinary beam with wavelength xcex1e of the first pair of input beams, a third collimating means for introducing a second input ordinary beam with wavelength xcex2o of a second pair of input beams and a fourth collimating means for introducing a second input extraordinary beam with wavelength xcex2e of the second pair of input beams.
The polarization beam combiner has a first wedge, a second wedge, and a +45xc2x0 Faraday rotator disposed between the first wedge and the second wedge. The first wedge, the faraday rotator and the second wedge are cascaded along an optical axis in a forward direction, and the second wedge is oriented 45xc2x0 with respect to the first wedge in the same direction as the rotation caused by the Faraday rotator.
A filter is disposed after the second wedge. The first pair of input beams is incident in the forward direction on the first wedge symmetrically with respect to the optical axis with a predetermined convergent angle between each other. These two beams propagate through the first wedge, the Faraday rotator and the second wedge, and then are incident on the filter. The second pair of input beams is incident in a backward direction (opposite to the forward direction) on the filter symmetrically with respect to the optical axis with a predetermined convergent angle between each other.
The filter reflects the first pair of input beams with wavelength xcex1 and is transparent to the second pair of input beams with wavelength xcex2, thereby the polarization beam combiner combining the first pair of input beams into a first combined light beam with wavelength xcex1 in the backward direction along the optical axis and the second pair of input beams into a second combined light beam with wavelength xcex2 in the backward direction along the optical axis. Therefore the filter multiplexes the first combined light beam and the second combined light beam into an output beam with wavelength xcex1 and wavelength xcex2. Also, the wavelength xcex1 equals to the wavelength xcex1o and the wavelength xcex1e, the wavelength xcex2 equals to the wavelength xcex2o and the wavelength xcex2e. The micro-optic system further has a fifth collimating means for receiving the output beam. Each of the collimating means can be a separate one for one fiber or can be shared by two or all fibers at one side of the system.
The first collimating means, the second collimating means and the fifth collimating means can share a first collimator, and the third collimating means and the fourth collimating means can share a second collimator. The first collimator is positioned before the first wedge, and the second collimator is positioned after the filter.
The micro-optic system further has a first subassembly holding an end of a first fiber, a second subassembly holding an end of a second fiber, a third subassembly holding an end of a third fiber, and a fourth subassembly holding an end of a fourth fiber. The first fiber and the second fiber are polarization-maintaining fibers being positioned before the first collimator and parallel to the optical axis. The polarization directions of the first fiber and the second fiber are 90 degree apart from each other for introducing the first pair of input beams. The third fiber and the fourth fiber are polarization-maintaining fibers being positioned after the second collimator and parallel to the optical axis. The polarization directions of the third fiber and the fourth fiber are 90 degrees apart from each other for introducing the second pair of input beams. The micro-optic system further has a fifth subassembly holding an end of a fifth fiber that is positioned before the first collimator and along the optical axis. The fifth fiber is a single mode optical fiber for receiving the output beam.
It is also apparent to those skilled in the art that this micro-optic system with such a design having a Faraday rotator, two optical wedges and a filter can be used inversely as a micro-optic de-multiplexing system for de-multiplexing an input beam from the fifth fiber with wavelength xcex1 and wavelength xcex2 into a first pair of output beams comprising a first output ordinary beam with wavelength xcex1o and a first output extraordinary beam with wavelength xcex1e and a second pair of output beams comprising a second output ordinary beam with wavelength xcex2o and a second output extraordinary beams with wavelength xcex2e. Under this situation, the second wedge is oriented 45xc2x0 with respect to the first wedge in the opposite direction as the rotation caused by the Faraday rotator.
The micro-optic polarization beam multiplexing system can further have a first polarizer disposed in front of the first fiber and a second polarizer disposed in front of the second fiber. The backward light beams of the first combined light beam from the fifth fiber are reflected by the filter and blocked by the first polarizer and the second polarizer respectively from entering into the first fiber and the second fiber. The backward light beams of the second combined light beam from the fifth fiber pass through the polarization beam combiner and the filter and become parallel to the optical axis, thereby being prevented from entering into the third fiber and the fourth fiber.
The micro-optic polarization beam multiplexing system of the present invention further has a sixth subassembly holding an end of a sixth fiber. The sixth fiber is a single mode optical fiber disposed after the second collimator along the optical axis. The light beam with telecommunication signals propagate in the forward direction from the fifth fiber, passes through the first collimator, the polarization beam combiner, the filter and the second collimator and then enters into the sixth fiber.
The micro-optic polarization beam multiplexing system can be used to provide an output beam that is a sum or a combination of the first pair of input beams and the pair of input beams for pumping a Raman amplifier. The micro-optic system can also be used to provide an output beam that is a sum or a combination of the first pair of input beams and the second pair of input beams for pumping an EDFA.
The filter of the present invention can be a grating, a thin film, or any other tunable and non-tunable filters familiar to those skilled in the art. Each collimating means of the present invention can have a GRIN lens, or a spherical leans, an aspherical lens or any other single or array-type collimators familiar to those skilled in the art.
The micro-optic multiplexing/de-multiplexing system of the present invention is not limited to handle only two polarization-perpendicular pairs of beams of different wavelengths. By any cascading or combining techniques familiar to those skilled in the art, the Micro-optic system of the present invention can be easily extended to handle three or more pairs of beams with different wavelengths.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The figures and the detailed description will more particularly exemplify these embodiments.